Human vision is capable of appreciating contrast ratios of up to 1:10,000. That is, a person can take in a scene in which some parts of the scene are 10,000 times brighter than other parts of the scene and see details in both the brightest and darkest parts of the scene. Further, human vision can adapt its sensitivity to brighter or darker scenes over a further 6 orders of magnitude.
Most conventional digital image formats (so-called 24-bit formats) use up to 24 bits to store color and luminance information for each pixel in an image. For example, each of a red, green and blue (RGB) value for a pixel may be stored in one byte (8 bits). Such formats are capable of representing brightness variations over only about two orders of magnitude (each byte can store one of 256 possible values). There exist a number of standard formats for representing digital images (which include both still and video images). These include JPEG (Joint Photographic Experts Group), MPEG (Motion Picture Experts Group), AVI (Audio Video Interleave), TIFF (Tagged image File Format), BMP (Bit Map), PNG (Portable Network Graphics), GIF (Graphical Interchange Format), and others. Such formats may be called “output referred standards” because they do not attempt to preserve image information beyond what can be reproduced by electronic displays of the types most commonly available. Until recently, displays such as computer displays, televisions, digital motion picture projectors and the like have been incapable of accurately reproducing images having contrast ratios better than 1:1000 or so.
Display technologies being developed by the assignee, and others, are able to reproduce images having high dynamic range (HDR). Such displays can reproduce images which more faithfully represent real-world scenes than conventional displays. There is a need for formats for storing HDR images for reproduction on these displays and other HDR displays that will become available in the future.
A number of formats have been proposed for storing HDR images as digital data. These formats all have various disadvantages. A number of these formats yield prohibitively large image files that can be viewed only through the use of specialized software. Some manufacturers of digital cameras provide proprietary RAW formats. These formats tend to be camera-specific and to be excessive in terms of data storage requirements.
There is a need for a convenient framework for storing, exchanging, and reproducing high dynamic range images. There is a particular need for such a framework which is backwards compatible with existing image viewer technology. There is a particular need for backwards compatibility in cases where an image may need to be reproduced by legacy devices, such as DVD players, which have hardware-based image decoders.